This invention relates to governors for internal combustion engine and particularly to a governor for an engine having a fuel injection pump, such as a diesel engine.
The governor for a diesel engine adjusts the amount of injected fuel to be supplied to the diesel engine thereby controlling the rotational speed of engine.
Various types of governor are classified in accordance with their mechanism such as mechanical or electronic, but these governors perform the same function, namely, to supply sufficient fuel to the engine for a desired engine speed. To perform this function, the desired engine speed furnished to the governor and the actual speed of the diesel engine are compared to produce a speed deviation from which an amount of injected fuel necessary for the actual engine speed to follow the desired speed in accordance with a predetermined relationship is determined by control and calculation such as proportion, integration and differentiation. The fuel adjusting plunger, or rack of the fuel injection pump is then regulated by a signal indicative of this determined amount of injected fuel.
In the diesel engine, at each fuel injection timing an amount of fuel corresponding to the rack position of the fuel pump at the fuel injection timing at each cylinder is injected into corresponding cylinders and consumed to generate an output torque. However in a case where the fuel pump rack is operated by a governor, the control of engine speed is actually made by only the rack position of the fuel pump at the fuel injection timing at each cylinder. As a result, the variation of the rack position of the fuel pump between timings is not taken into consideration in the control of the engine speed.
Also, in the diesel engine, since the output torque is generated by the explosion of intermittently injected fuel, thus torque pulsates in accordance with the number of explosions. That is, when the diesel engine of Z cylinders rotates at a rotation speed N (rpm), the output torque pulsates at the period of 60/N.multidot.Z (sec.) for a two-stroke engine, or at the period of 120/N.multidot.Z (sec.) for a four-stroke engine. As a result, the engine speed pulsates at the same period.
The conventional governor of a diesel engine is not intended to control the periodical variation of engine speed due to the pulsation of the output torque generated by the diesel engine itself. Moreover, however the amount of injected fuel is adjusted by the governor, the output torque of the diesel engine cannot be prevented from pulsating.
In addition, even if the governor controls the rack of the fuel pump in response to the periodical change of engine speed due to the pulsation of the output torque, it repeats only useless operation of the rack because the operation at a time other than the fuel injection timing is useless.
Therefore, it is desired that the governor of diesel engine should not be affected by the periodical variation of engine speed due to the pulsation of the output torque generated from the diesel engine itself. In the conventional governor, however, any countermeasure effective against that problem is not made yet.
A governor may be proposed in which a mechanical or electrical low-pass filter for the engine-speed signal is provided so that the governor does not respond to the periodical speed variation due to the pulsation of the output torque generated from the diesel engine itself.
In such a governor, however, since the period of the engine-speed variation is changed in proportion to the rotational speed, the cut-off frequency of the low-pass filter must be decreased to remove the engine speed variation in the low engine speed range. Therefore, this governor arrangement suffers a deterioriation in its control ability at various engine speeds by the effect of phase lag in the low-pass filter, and as a result the control of the engine speed is apt to be unstable.